Electrical sound recording, reproducing, and like apparatus



A. F. SYKES Dec. 9, 1952 ELECTRICAL SOUND RECORDING, REPRODUCING, AND LIKE APPARATUS 5 Sheets-Sheet 1 Filed Jan. 20, 1948 l] u H A. F. SYKES Dec. 9, 1952 ELECTRICAL SOUND RECORDING, REPRODUCING, AND LIKE APPARATUS 5 Sheets-Sheet. 2

Filed Jan. 20, 1948 EM wmm ag 5 Sheets-Sheet 3 A. F. SYKES ELECTRICAL SOUND RECORDING, REPRODUCING, AND LIKE APPARATUS Dec. 9, 1952 Filed Jan. 20, 1948 1 6 A War flMfiZm-M, W

A F SYKES 2,621,260

ELECTRICAL SOUND RECORDING, REPRODUCING, AND LIKE APPARATUS Filed Jan. 20, 1948 5 Sheets-Sheet 4 Dec, 9, 1952 Dec. 9, 1952 F. SYKES ELECTRICAL SOUND RECORDING, REPRODUCING, AND LIKE APPARATUS Filed Jan. 20, 1948 5 Sheets-Sheet 5 Patented Dec. 9, 1952 ELECTRICAL SOUND RECORDING, REPRO- DUCING, AND LIKE APPARATUS Adrian Francis Sykes, Saint Albans, England Application January 20, 1948, Serial No. 3,307 In Great Britain January 24, 1947 9 Claims. 1

This invention relates to mechanism for electrical sound recording reproduction and the like by means of magneto-striction. In certain of its embodiments the invention makes use of magneto-strictive rods polarized by a magnetic field and operated by acoustic currents in such a way that as one rod expands another rod contracts and hence the two actions, although in a sense cancelling, in fact result in twice the degree of vibration of one rod alone. This system permits the terminal relative vibrations to be brought close together, which is an important consideration. In one case the vibration is resisted, or reduced, by the inertia of a mass of material, or floating weight, and a double vibration is felt at the free end of the rods. In another case the two ends are so anchored in common to a mass that the free ends of the rods may give rise to rotational vibration. Apparatus of both types has been built and successfully operated experimentally.

The incorporation of what may be regarded as a push-pull construction is considered to contribute towards the linear operation of the devices in action, though in some cases because phase opposition is obtained mechanically the action is really push-push. In both methods the supporting structure is largely relieved from the vibrations. At the same time the push-pull method, as appears hereinafter, tends to cancel out thermal expansive changes which may be a source of annoyance and error from the point of view of sound recording when the positive or sliding shoe system is used.

The minute range of the magneto-strictive phenomenon renders its useful application at first sight singularly unsuitable for practical acoustic purposes; and, indeed, such does militate against its use. Nevertheless I have succeeded in large degree in producing an effect sufficiently free from distortion and of enough amplitude to apply to sound recording, telephony, deaf aid, and, in a minor degree, loudspeaker reproduction. As an offset to the very severe amplitude restriction I, in general, add a mechanical amplification system (e. g. lever). This is practically possible since with suitable proportions althrough the actual movement is slight it is at the same time of a more or less irresistible nature. Mechanical amplification results in a great increase of apparent mass with each increment of enlargement; hence the lever system, sometimes compound, requires to be carefully designed, light in Weight, small in size, and as rigid as possible. In this specification the magneto-strictive material is referred to as nicket but, of course, nickel-iron alloys and iron itself, especially when used in strong tension, can be substituted.

Nickel, as is common knowledge, contracts in length up to a point if placed in a magnetic field. The contraction and expansion as the case may be is not regular throughout the range of field strength; but over a part of the range it may be regarded as sumciently proportional to the change in field strength for acoustic purposes,

There is also the possibility of correcting for, or reducing, linear distortion by suitable methods of working. In particular in this invention the use of mechanical push-pull and the control of the fiux values by means of a constant potential system of electrical operation, aided by negative feed back, has resulted inv the production of apparatus of rather unexpected precision. The term rod is used to denote the magneto-stric-. tive elements when in fact the actual construction is a laminated and slotted closed magnetic circuit core, like an elongated choke. I have made numerous models experimentally with plain rods, both of open and closed magnetic circuit type but for use on the constant potential system is a laminated closed magnetic circuit core is preferable. With the closed magnetic circuit the full force of the hysteresis in nickel is experienced and it is the function of the method of constant potential, as may be likened to an electric supply which can provide a variable load without much drop in voltage, to render hysteresis nugatory. It is possible to provide the requisite polarizing field externally by a solenoid or by a separate winding over the speech coils. This procedure is practicable but the direct superposition of polarizing current is favored. A further alternative is the use of a permanent magnet.

In the application of the present invention I shall describe apparatus utilizing the gridiron, or re-entrant, principle; the method of common anchorage of multiple rods; the method of squeezing by thrust rods from the ends of a magneto-strictive element. All these devices are aided by mechanical enlargement. A further method is to use a rod or rods arranged to yield lateral vibration either by elastic flexing of the material or by linkwork construction which further method provides for mechanical enlargement in virtue of the constructions themselves. The idea behind these four methods is to bring, or lead, the terminal vibrations of the expanding and contracting material, which are widely separated, as close together as possible so that the.

motions can co-operate to actuate a stylus for the purpose of engraving or embossing a blank. As the vibrations obtainable are all too inadequate every eiiort is required to make effective use of such as there is. There would be little point in employing long rods because of resonance in the material and supporting structure and then other methods would be more convenient and effective. Since a nickel rod of a few inches in length has a natural frequency of many thousands a second, say 10,000 to 20,000 a form of recorder of aperiodic nature is readily obtainable but without some magnification the amount of vibration is too small in practice.

A telephone receiving device, based on magneto-striction, is mentioned by Silvanus ThOIIlD'. son in his book Elementary Lessons in Elec- 3 tricity &-Magnetism-, 1899, pages-540 and 541.

There isa'p'aper'by George W. Pierce in the journal of the American Academy of Arts and: Sciences, volume 63, 1928-9, on the subject of" magneto-striction as applied to standards. of frequency. K. Charlton Black also'h'a's' a'paper in the same volume and mentions various magneto-strictive materials. Magnetmstrictivegraphs are shown on page 663, volume 14; of the:

Encyclopaedia Britannica, 14th edition.- The.

explained in connection with-the accompanying" drawings; in which: I

Figurel is a composite andel'evational-view partially broken away and illustrated in section showing one'embodiznent of my invention; the

view including a: schematic electrical circuit;

Fig; 2 is a top plan view of the embodiment of my invention shown" in Fig. 1; Fig. 3 isa fragmentary view' partially in section and partially foreshortened; showing the relation" of theseveral electrical windings associated with the" magnetic circuit of the embodiment of my invention shown inFigsz'l and" 2; Fig; 4 illustrates" a side elevational view of oneform of mounting: for the embodiment of my invention illustrated" in Figs". 1-3; Fig; 5 is atop' plan view of the assembly shown in Fig; 4; Fig; 6 is" an ele'vational view' of' the magneto-strictive rods employed in the form of my invention shown in Figs; 1-5;" Fig. '7 isa fragmentary view" showing the details of the connection of the upper ends of the magnet'o strictive rods; Fig. 8 is a schematic wiring diagram of the circuit employed in the embodiment of myinvention illustrated in Figs. 1 1; Fig. 9a is a fragmentary cross sectional view showing the manner of connection of the lower adjacent ends of the magneto=strictive rods; Fig; 9b-is a plan view of the assembly shown in Fig. 9w; Fig. 9c is an end'elevational view of the assembly shown in Fig. 9a; Fig. Set is an end elevational view looking in a direction opposite to that direction from which Fig. 9c is viewed; Fig. 10- is a detail view of the retraction mechanism associated with the recorder; Fig; 11 is an assembly view of a modified form of my invention partially 4 shows an application of thee magneto-strictive device of myinventiondn. the operation of a loudspeaker.

Figs. 1,, 2 and 3 of the drawings relate to an: electrical; recorder suitable for a cylinder machine (or for a hill and dale disc machine) but they also serve the purpose of general description. .The magnetic field is provided by a rectangular double layer solenoid I, wound on a rectangular copper tube 2, with ebonite cap 3 and copper cap- 6. Terminals 5 and 5 indicate the ends of this field coil.. Thiselectric solenoid is secured to the pierced" ebonite. surrounding block" I which in turn is held'bythe.

brass plate 8 provided with pivot: brackets; as

at 9* and supporting lug .33" held". in" the reproducer'post 34- of thephonograph: The type strictive motor in the form of my invention to the magneto-strictive members; 1'7 a schematic view of the circuit employed in the form of my invention shown in Figs. 14-16; Fig. 18 shows a further modified form of circuit which may be employed in the form of my invention illustrated in Figs. 14-16; andFig. 19-

of phonograph for which this apparatus istsuit' able is known as the traveling mandrel type. in whicl'i"v the reproduceris fixedand the" record is traversed beneath; Nickel rods (annea1ed)' Is and H, over-wound with a single layer of cotton covered copper wire (marked H oniFig 3) aremounted'on" the floating weight l2.and': secured by set screwsas'at I3. These set'screwshold the rods Hl'but. not the rod II. which. is fixed to the. bridgepiece; l4. at" one end, while the other end passes through the rubber hush It in the floating weight l2. The windings H are connected in series so that the two outer rods increase in length. by' change. of current while the central rod diminishes in lengthand vice versa, that isto: say that the central winding' is so wound orconnectedias' to. be of reverse polarity or the? rod of different material. Thev end or" the nickel rod H is kept in'engagemcnt with the .stylus lever 18' which is set between pivot points as at [91' by the tension spring 2i? kept stretched between the'binding post 21' and a bell crank". extension '22 of. the stylus lever.

lhe support 2.3 for the stylus lever pivots is suitably recessed to accommodate the parts. Further" pivots as at 24' permit the. floating weight to rise andiall and the. solenoid is sufficiently large to allow the nickel rodsto sway backwards and forwards without touching. A stud 25' acts. as a limit stop in conjunction with the raising mechanism which is comprised by a brass block 25, rotatable knob 27' andspri'ng' blade 28" which is depressed by eccentric action; To set the depth of cut in the wax cylinder 29 (or in the disc) a slide ball 39, shown. raised for convenience of drawing. is provided; and.-.a fine adjustment is secured by rotating slightly the whole apparatus about the axis. 31 by micrometer screw (not shown) or otherwise and clamping in the desired position. The. solenoid circuit is operated by a battery 32, rheostat. 36 and amperemeter 31 so that the field. strength can be adjusted either by theory (that is from the magnetic curve of the material) or by trial and error to the bestwal'ue. The circuit ll'is connected by slack wire to terminals as at 35.

Fig.2 is a plan view of the top solenoid cap to indicate the shape.

Fig. 3 is a fragmentary view of the floating weight l2 and the overwound nickel. rods. 'It also" shows the method of mechanical amplification which may provide an amplification ratio of 3 or 5 to l.

The apparatus illustrated is not merely one proposed but is in good proportion and based on an actual experimental construction, the result of, numerous experiments. With this apparatus 11 have made a variety of sound records from radio transmission, and also from other records by means of a. pickup. The movement also, in the course of testing, has been used to operate a phonograph reproducer (by application to the stylus and lever system of the reproducer). It has also been used to work the cone of a loudspeaker and applied directly to a. three ply baffie board. If the end of the rod II is held in the teeth a strong reception is realized and this end may also be applied to the ear with or without a cap. Similarly it may be applied behind the ear.

I have tried various gauges of nickel wire or rod from one half millimetre up to one eighth of an inch diameter. Various lengths of wire or rod have also been tried. My early experiments were carried out with the small gauge wire covered with rubber (for damping) and overwound with enamelled wire. In the drawings herewith the nickel rods I0 are one eighth of an inch in diameter and the rod II is one sixteenth of an inch. The effective length of each is about seven inches. Better frequency range however is obtained by a reduction in length to about 2 which provides a higher natural frequency. With the ordinary wireless set, and with suitable winding H to match the impedance, effective records of wireless programmes can be produced. The rods are wound with No. 28 S. W. G. double cotton covered copper wire.

The invention is not restricted to the arrangement of rods shown in the illustrations. Other methods include rods fixed at one end but free at the other, which arrangement seems useful for the production of apparatus for cutting lateral or Berliner records. It appears desirable in recording and reproducing to make use of tone control to diminish the response in the upper register. Electromagnetic apparatus is usually reversible, that is to say while currents produce movement so also movement may produce currents, and thus apparatus designed for recording may give rise to designs for microphone, pick-ups and the like.

Other embodiments of the invention use multiple rods with a common anchorage. I have carried out much experimental work on this system which has led to the production of apparatus capable of fulfilling in a higher degree the requirements necessary for high grade sound recording. The magneto-strictive system shows some striking qualities in that a high natural frequency, of the order of 10,000 periods a second, is readily obtainable, and at the same time the stiffness of the members is great and the operating forces relatively enormous. Hence the cutting stylus can be firmly held in engagement with the wax blank and mechanical amplification is a' ternating current machinery. The speech coils are treated as inductances and the load on the amplifier is intended as far as practicable to be wholly inductive. The current therefore, other things being equal, falls with rising frequency but 6 the change in flux, on which the extension 01' the rods depends, closely follows or corresponds with the wave form of the potential or voltage when the latter is integrated. If desired, to produce a brilliant (or sharp) record the valve amplifier is set to differentiate and thus compensate for the choking effect of the speech coils. Alternatively a form of microphone itself may have the necessary characteristics. Without such provision it is obvious that large amplitudes in the bass will use up the available range of either record or recorder before a useful degree of loudness is secured. In reproducing the bass values can be recovered by condensers, tone control in general, integration, and such like artifices. Moreover small amplitudes in the treble involve confusion with the surface noise or scratch, while with preit the response in the extreme bass by the inser-- tion of resistance or the predominance of the impedance of the output valve or valves and to give ere-emphasis in the treble to avoid surface noise. It is regarded as good practice to introduce all tone control in the amplifier circuits prior to the output valve in order to give the constant potential system full scope. At the mechanical resonant frequency the speech coils are, in effect, short-circuited by the output valve circuit, aided by negative feedback, which provides electric damping. If desired viscous damping can be provided in addition.

The apparatus consists of two rods side by side, and as close together as possible, with one pair of ends anchored to a structure, the floating weight. The free ends are linked together by a stylus lever, simple or compound, with pin joints or the like, to produce angular or rotational motion, and a roller is set between one rod end and the floating weight, with spring tension, to take up the transverse thrust. A springy leaf is an alternative. The symmetrical construction provides temperature correction. The rods are overwound with one or more layers of No. 28 or No. 30 S.W.G. double cotton covered wire. Each rod forms a closed magnetic circuit, either in virtue of junctions or a slotted construction, and constitutes a choke. The windings are in opposition so that as one rod expands the other contracts and the polarizing current is led in at the junction of the speech coils so that a battery and con: trol resistance can feed current to the coils in parallel and the return is through the center tap of the amplifier output transformer. The circuit for the speech currents and that for the polarizing current could be interchanged. The depth of cut in the wax is determined by a sliding shoe with micrometer adjustment.

Figs. 4 to 8 inclusive are concerned with the instrument just described as a Whole together With certain details and circuits. Figs. 9a, b, c

and d and Fig. 10 illustrate small parts to an enlarged scale.

Figs. 4.- and 5 of the drawings represent side elevation and plan views taken from above a magneto-emotive recorder constructed on the basis of two rods set side by side, and as close together as practicable, with one pair of ends anchored to a structure, the floating weight l2. The free ends are linked together by a stylus lever system i8 of compound type, with pin joints, pivots or the like as at !9, to produce angular or rotational motion, and a roller I33 is set between 7 see we. the. fleetin we ht. '23 ith. ta ie. t brewer??? el and; t lqeli cqnst tsa. atu e q re tipnq hemes a l e sf isn tree T .t unct ns. r.- slpt ed; qs t uc en. fonstitutes a form of 1 er e r he pe w: m st. a k 'rreet P d ces: bothrods. but a superposed current 1 he h qeetr t iq m ne od. etra tionie heoth ChiQ n ileu e ire hi t r i e t-thedeuble. erelt er e tone.

ndicatedtat l'le Thev s are.

- e. ads not wn, wl ed: ed bla k n green ='e. e. 7ta tsue rqm. he ol 3.91 n. t e. t all block; a refinement to, he. used at. ne re upp eme tar w i .0, iarat velx. few turns. is'overwound on the .9 e tlf h eae ive l a of t y tem. n equ s s e est es. ne a in e a ,e. objector; this device isto.

w. i: hepee by end: to leem a relies-e? Q51. e ut rans: a e streameda am Op P Y; .Q t5?-Qn t e p emen rr w nda ing. The total turns on the speechcoils, threaded lgyhand. to avoid junctions in the magnetic cirit" isof the order. of 800 so the number of turns elsupplementary winding, which is similar, be about 100 When this device is not in use a. negativeff eedf back to the amplifier is taken from 'afpot'ential divider. on the secondary winding -o ftheoutput transformer itself and tends to produce a constant potential system whereby hysteresis'efi'cts are nullified as occurs in ordinarfpow erl transformers working on a public. supply: I-lireJthe secondary output voltage is a copyof-the'primary input voltage as is explained in the book .Electro-Magnetic Devices" by HG. Rotors (1941 pages 19 and 20) notwithstanding hysteresis. This desirable state of aitairs onlyv g; in the main the reaction of the speech coils is inductive. To continue the description of the drawings, the floating weight I2 isj coinpiosite in that attachments 4| and 42, whiclfcciuld beintegral; appear. The attached ib -154i, fl'x'ed byscriews as at 55, holdsthe rods and eneag stitn pivot points 24 and the lower block!) channelledforthe accommodation of th compound lever, systemlsand the slide 43, with cla'rnpingi' 45, also for. the tension spring 26 andhnicrometer screw 44. Both the clamping. screw 45 and micrometer screw 44 act on an inter al bridge'piece' The slide and diagrammatic -;s'hoc3lare shown withdrawn for clarity. This slide. provides, for coarse adjustment of the depth of cut. 'The'wh'ole system engaging, in this insta nce, with the side ofthe cylinder 29, fits conveniently on the type of Edison phonograph indicated'and "is carried by the slotted block 9 reston asupport 8 and rotates to some degree about the shouldered screw 46 in response to the movement'ofthe micrometer hand wheel fi'l whichengages with rod 48 and the movement; is r e's'sted by the spring 49. This method of rotatie "is awell'proved and useful method for. con: t ai sth d th 9 ti tthe b e A a e t ees-"Q ite. .1 his;

ow reque cy: nflu q 0t 8; 5.0,; in. en a ement; wi h} rin q e qll n. we. 5-. a d reat by t efie e m h nd. le ter, 3-. Prev; 1 me ns. iot n a hdrawin he. t us. ever.- t. i h. he blank- Fig. 5 isa plan viewfrom above.

Fi fishon tlie mpi ssfe ivi eat da /100? h ck slot en th. 2, l'rhu t untagebqgt. /5 to form rods Band. Lila. and also ,thelinkworlg. attachments 56,-and.5;1. Both limbsare. wound;

Fig. illustratesthecattachmentoi thernds. Ill? and; I Detothe block! t Figure. 8. is concerned, with. the. speech coil. circuits. Here the two (ring) windings I1, are. joined inseries, the junction constituting a center tap. From this center. we (the green wire) a controlling. resistance 36,"ammeter"31; "and; bat.-' tery 3 2: of alkaline type'donne'cted to the center tap'ot the choke53, which latter may or course Bethe qutputtran srormer' itself; ie'centeritap e accept ohms and the polariiifigburrefit is orthej order or 1:2 amines- 1. 01's amps'pe; Sign of;

A Figs. 9a, b, c, and d refer, to the details or attachment ii! and vari'oiis' asse' n Th n si eel we n osether 9s; i- .1 s. a e iron}. he. eboye i the ttac meet it ndicat the at Qt the zniem 9i 'ns.-wh h..mtovi.des m.

2: the. various detai sand ocki s rews as 3415. for th damn-f nsi d e andni mt rode, t e. top. v ew. of. the bracket 6L n of; the lower. lever; in th stylus. lever. ystem 1.8. showin central milling. to. ensure. contact with the pivots 64, which have a: slight. shoulder at theiends. to. friction.

Eig, 9c, is a partialview of: the attachment lz. and system. as seen from the face of. the. blank.-

7 F Here. the top stylus lever is seen. set. between the damping faces. 54; the interspaces being filled in with boiled castor\ oil. Ddtted lines at. the top indicate the'trace of: the speech coilsf'lfll' The eccentric mounting of the sliding shoe. or, ball appears at. 3!}. Thisistoproivide adius'tmntzfor lining up. with the edge oi. the stylus. The lower. stylus lever. is shaped for, lightness and strength and the. dotted curves indicate an alternative co tourthe 9d s a f a menta View similar to Fi 9c.

' as. showing. he. nature Q hem lei1 whos 9 in place. The dotted trace 61 refers to the housing room for the rod 48 of Figure 4.

As in all amplitude limited systems, including records themselves, the frequency-amplitude characteristic requires consideration. For small amplitudes and direct reproduction from the blank itself with little surface noise an approximation to a uniformly falling characteristic, the analogue of the displacement wave of the sound, can be realized. For the production of loud records fully recorded the position is far different and it is desirable to cut the bass and emphasize the treble, subsequently restoring the balance in electric reproduction. This matter is well known and the proportions and methods that can be adopted are legion. For instance the bass can be cut in the input by a circuit containing a condenser and resistance so that the output rises up to a frequency of 400 cycles per second or more and the treble emphasis can commence at 1600 cycles per second by means of a resistance and inductance circuit in a valve circuit in the amplifier on the lines of the British specification No. 160,223. Again a complete or a modified form of differentiation giving a sharp record can be made and subsequently corrected in the reproduction. Obviously the blank can be what is known as wax or it may be faced with cellulose acetate or even soft metal for embossing or otherwise.

Some remarks may be entered on the subject of the magnetic state of the cores. Before recording the polarizing circuit may be repeated reversed, commencing at a higher value of current than it is intended to use. As after switching off and then remaking the circuit a different magnetic state exists it may be desirable to take this into account by switching on at a higher value of polarizing current and then reducing to a chosen value as a routine. Used without polarizing current, aftersuch has been used, the instrument will still function for weak recording but is more or less completely demagnetized by strong passages and much distortion is then introduced together with feeble response. The

mean value of the flux density in each rod will change notwithstanding the polarizing current from wave form to Wave form but it is considered that the push-pull action prevents any serious out of balance as a whole. As sound waves are complex it would seem likely that the harmonics assist in ridding the fundamental of a note from hysteresis, hence pre-emphasis in the treble may have a beneficial influence in that supersonic harmonics can be brought to bear. Recently the use of superposed high frequency currents for magnetic recording on a steel wire has come to the fore. This idea may be useful for the magneto-strictive instrument, especially where it is sought to use it as an oscillograph or oscillograph type of recorder where the signal current is driven through the speech coils. To do this the speech coils work in conjunction with a high impedance valve circuit in direct contrast with the method of constant voltage (relative) as in an electric lighting system developed in this specification.

In another form of construction which aims at simplicity, a single compound rod of closed magnetic circuit type is gripped at the centry by the floating weight and virtually forms two rods in opposition. This is analogous with an air pipe resonator open at both ends with consequent'rise in natural frequency.

In this way there is not the same tendency to vibrate the structure (floating weight and supports). The vibration from the ends, which is in contrary phase as in the other constructions, is brought to the center by light rods of aluminium or Wood, etc., and operates an elastic mechanical amplifier of the slack wire class producing vibration at right angles to that of the rods themselves. This mechanical amplifier, although there is a difference, resembles the hot wire ammeter movement but is fashioned from sheet material, very small in total mass, and forming two sides of an open triangle with apex close to the (imaginary) base. A motion of the rods together produces a magnified movement of the apex. In fact the action is by squeezing. The apex, either by direct contact or by the intervention of a transmitting strut, vibrates a small elastic tongue or lever which carries the stylus. To take up the transverse thrust two elastic strips (or rollers) are provided at the ends of the thrust rods of wood or aluminium which engage with the mechanical amplifier. The strips are anchored to the floating weight. For this arrangement to work in practice, except by the device of floating the whole gear on the wax blank itself, a practice which is not very desirable, it is necessary to make the floating weight in two parts. The first part, pivoted on the main floating weight, carries the sliding shoe and the elastic tongue (which may be likened to an aperiodic diaphragm) with attached stylus. The main floating weight with magnetostriction rods is supported on the elastic tongue and so causes an elastic deflection of the tongue, aided by spring action for stability, and an oil dashpot links the two masses together and locks them except for slow correction for any thermal expansive effects. For adjustments of the depth of cut the tension of the spring pressing the two halves of the compound floating weight together can be varied and thus the degree of deflection of the tongue altered. Alternatively the whole recorder can be rotated about an axis by micrometer screw. The attachments are proportioned so as not to reduce the high natural period too much. To bring about the condition that the inductive impedance of the speech coils, which are in series, is large as transferred to the valve circuit a high step down ratio is provided in the output transformer. Use may be made of negative feed back to assist in this matter. Polarizing current is obtained by a battery and control resistance in the secondary circuit of the step down transformer. It may be noted that on reducing the polarizing current to zero the flux in the nickel remains at a relatively high value and hence to realize any thing like the full range of operation this state of affairs must be taken into account. The signal, or acoustic, currents must be able to overpower the polarizing current and so be able to act in the left hand top quadrant of the magnetic cycle diagram. It is this consideration which brings out the full significance of the constant potential system. Thus the value of the polarizing current is a matter for experimental determination.

Figs. 11, 12 and 13 describe in detail the apparatus as above. Fig. 11 shows a compound floating weight 12, with tail piece 81, and l2a articulated by the pin 68 so that the parts can separate or close with freedom. The weight or mass He carries an adjustable rod 69 secured by a set screw 10. This rod is screwed into the counterbored dash-pot element H working in the oil containing dash-pot chamber 12. A

lighttube orchimney; laiallowsfree motion; and;

serves topreventleakage on oil. For. all: acoustic: frequencies the parts lZand. 12aare-lookedz together by the oil,;which: latter is. notfor damping;

butto permitakind of breathinga'ction for'slow' thermal changes, without. any alteration. of. de-

flection of the stylus: carrying element; To the.

lower' section. l2a; of: the. floating; weight is; ate-J tached a. small extensionil ito which is.soldered-..

or otherwise secured, thespringyblade 15 car:- rying the stylus.

gripsorclaws-asat 16 in Fig. l3 for. holding the magneto-strictive motor l0, Illa formed; in. one;

piecefrom purenickel-tape 1%" wide and M thickto. provide: for alaminated? construction;

The total length: of the magneto-strictive rod. is about 13 .5;cms; andrthe effective length. about 12-. cms;, that is. to say. about: 6: cms-.. of the rodi ex! tend'xont either side of? the: support as; will: be,- clear from the figure. A: thrust; member or strut.

59; conveys: vibration from the mechanical am:-

plifying device (squeeze amplifier)v 8llto'theablade1 15:. The: squeeze amplifier 80; is: actuated'bythrust .rodsas. at H a in; Figure. 13. The: whole: composite fl'oatingstructurexis. setv on a pivot. axis .Ztinthe-"slotted bracket 9: which; is held.

by:the-(lug3.3:1about'zwhichiitiis free to rotate in small degree: in. response togthe springresisted micrometer hand wheel. 4.1; .asa fine adjustment for the; depth: offcutzin the blank; The member- I 7; serves. as a: cap .tothe lug 3 3' but atthe-r same. time; provides for theretractive device 1B'..acting; onthe U: loop'flll and controlled by,the hand IGVBIEZL. Aspring'88ikeeps the parts. l2: and: l2a'- pressedtogether apart. from gravity butv is,noti:

essentialito' the action; Figs. 12:: and 131 should be considered together;

Rig; '1'2318 amelevationbut-at: right angles to: hat of Es -11. and. shows;.the; masn torstr ctiv l m nts tend! Ba, aetua l es. a1 ton$. deda dbe na eteaszwou dr be t na i e: h

A sliding shoe; (omitted inEigt. 11) is:also provided;. Theupl er: weight i2 has:

transmission rods J {a wh ich canbe nickel but. 1

which do not carry speech .coils the squeeze;ele-

ment{ B0, sortatransyersei gripsflZ for the rods] I a,

ball .30...

i i e me ew- Plan ew her e z r ing. mechanismes. viewed from beneath; This,

shows the magnetostrictive core; i 0 and; Bct;

woundifrom, nickel tape as app.e'ars at. 85 which. indicates layers and theendsflfi It. also Shows- 16; indication of 's'peech'fcoiljor coils a sjat ,I .i which.

constitute, aLlQSinglL Of fi-lllti layer. ring wiilding.

over the nickel pore, transverse ,grip'sas at. 82;.set screws as at 8'3. anditightenihg, screws as, at 8.4 m

transmit the vibration; A, portion of ithe'j..uliper, floatingweight I 2 is indicated and the hole or chimney which allows the rod 69 of Figure" 11 to,

pass through isshown at-IS; 7

As' the thrust-rods H a;already vibrateautomatically in oppositephase-it -is not-necessary to divide thepolarizing current for the core. Thus this polarizing current traverses the; winding l 1 and'the secondary winding of theoutput trans former with a battery and some control 7 resistance inthe circuit for {regulatingthe current.- The windings should be designed so that; say, with-a single alkaline cell, chosen because it does not" lose charge when'idlefor along period; a mini-- mumof inserted resistance. appears under work'- ing conditions. r

'45 le-s ide W13 i. nd-- c u terb ance s rinafli; to, reducethe weight tobe; borne-by; the slide.

12a Therecordercanbe operated;without. any theoeretical considerations but. preferably. with; some. tone control. in. the amplifier. There are; however, two well' defined methods: or. working; In

a. the first, which. is favored, the wound;v core is treated asan inductance andsupplied withco n'e: stant voltage (relative to the acoustic changes) notwithstanding that the current mayvary over: aWiderange. This requiresan amplifier of;ccnsiderable available output of'which only'a small. part in volt amperes' (inductiveiload) is taken. A negative feedback circuitassistsvery much the attainment of this conditionasit tends to-im-- provethe' regulationof the output, that to say-- the maintenance of the terminal' volts undervary ing conditions as though the output circuit '(hightension) were devoid of'internaliresistance, which would'be thecaseinan ideal 'forrn of valve-.- A

step'down transformer with-aratio of 50 to 1 en ables the valve-system to supply the-heavy currents in the bass where the inductive impedanceof-the loadis so small.

The-second method is to drive theacoustic cur-- rents through the inductive load by the use of a v high impedance output circuit and to rely on the harmonics; perhaps the supersonic harmon ics, to rid the core of-hysteresis. superposed high frequency oscillations can be'addedfor the same" purpose; In this second methodthe record is'of course of relatively brilliant type. other things beingiequal.

It is considered equivalent and": far preferable to differentiate the acousticinput and then allow theinductanceof the nickel core'to integrate the efiect' of the. output volts operating on the cone stant potential system.

A fourth general methodofdisposing thenickel rodsto operate a recorder will now-be described. Here the rods are disposedin virtue. of;flexing,

or equivalentlinkwork", so as .to provide lateral" vibration in magnified degree and thus yield an enlargement of vibrationfrom the rods. them-.'

selves. At the same time. this] procedure results. inthe desired co-operation of therods to bring. the ava'ilablevibration' toapoint or in closelpro'iie unity.

These devices are simpleto. construct andfopera ate ,andfveryj cheaptoproduce; moreover they are.

very robust and stiff, thatlisto saythe-stylus is.

hield injri'gid. fashion like a lathe'tool as con-. traste'dwith the action ofa sensitive diaphragm. This, latter. consideration is very. favorable. for! hilL'andidale recording; The. term.rod as bee.

fore to be understood broadly and includesa -bundle of bondedwires or slotted. core .stampings,

aridjs'o'on. The magnetic circuits can be open... or closed as in a choke. Considerations of. eddy}.

currents and hysteresis arise and alsothe methods of; operation having regard to the inductanceor;

the wound rods and'the recording characters tic's desired: I. have already dealt" withthes'ef matters and donotr'efer to them. again in the dej scription which follows.

Figure l4ofithe drawings. shows a simple an effective} form of i the invention whichfrequires. littleskill to construct ;or knowledge 4 tobper'at'e. Nickel rods; m and 10a; forming onenengtnfor material fin'prac'tice; but not llCGSSElLliIYiflQCOIl-l ception, and constituting a' U -o'r'V areigri'pped'i in setfscrew'holes; or} by plateain the floating or swinging weight-l2? A single or multilayer? of "wife; say'No; 2 8 SlS.'G.;. is "overwoundfon the,

rods as shown dot-ted" at H and. a mid-point tapp ng is broughtout fat: 98. Hill .an'djdaleor. Berliner stylii '91 areattached 'as'shown and the '13 apparatus is pivoted at 24 for floating, with or without counterbalance, on a blank for recording. ()bviously the axis must be altered to use the Berliner stylus. At Fig. 1'7 a circuit diagram is shown which provides for a polarizing battery 32 and control resistance 36, and also a center tapped choke 53 which may be a winding of the output transformer. This circuit is for the purpose of allowing the nickel rods a mean, or suitable, contraction so that the series current from the output transformer permits the rod ID to expand and the rod Ina to contract and vice versa. This relative vibration causes the apex of the U or V to vibrate transversely, and in magnified degree, according to the proportions chosen. The device represents in good proportion actual experimental apparatus in which the height of the V is about 2 the material nickel wire 2 mm. diameter, and the spread of the base about A". Applied to the teeth a strong and intelligible reproduction of sound is realized and the range is considerable. It works from the normal output of a wireless set preferably with some degree of tone control. To level the load a resistance, equal to that of the loudspeaker appropriate to the wireless set may be used in parallel. If the weight l2, which may be read as a plain cylinder or pair of plates, is of nonmagnetic material then the magnetic circuit is open, while if the material is iron the magnetic circuit is substantially closed. The apex of the V could be formed by a pin joint in which case the rods and Illa would be actually separate pieces.

Fig. represents the basis for a design for apparatus whose action may be likened to that of a bi-metal strip for temperature. It is actually a. derivation from Fig. 14. The rods l0 and Illa, parallel and close together or spread as in Fig. 16, are housed in a channel 94 in the floating weight l2. The rod ends are bonded at 92 and anchored by the stirrups 93 and rollers as at I36 with central bonding by the insert 91. The anti-phase contractions and expansions of the rods cause the center to vibrate transversely in amplified degree and the device is worked on the basis of the circuit of Fig. 17. The rods may in fact be slotted cores, forming closed magnetic circuits, built up from bonded stampings, that is laminations, or similar shapes of solid material. Fig. 16 is the basis for a simple design with bent rod the anti-phase motions of which cause transverse amplified vibration at the center. The bent rod with sections I0 and [0a, overwound with wire directly or on bobbins which do not touch the rod, is anchored firmly, as by soldering, to the mass I2 and operates directly by the stylus 9| or the weight I 2 may be fixed to a feed carriage and the vibration transferred to the stylus by the conventional old style Edison method indicated, by cord or link as shown. In this case the stylus 9| becomes what is known as a crosshead.

Fig; 18 shows the appropriate circuit and requires no further explanation.

Fig. 19 shows the movement of Fig. 14 as applied to a form of loudspeaker for miniature reproduction, of interest in scientific demonstration of the acoustic application of nickel and like material. It should be noted that the vibration is applied at right angles, or tangentially, to the periphery of the curved paper or cardboard (say Bristol board) sheet 95 which may be stiffened in the immediate vicinity of'the application of the vibration. The ends of the spread U vibration motor are bent parallel in this case to slide into set screw holes in the mass [2 which could, of course, be the casing itself. This method of impulsing at right angles is experimentally more efiective than the direct application in the normal way. The talking sheet is held in the casing or baffle 96 the sides of which may be plush lined to grip the sheet lightly. The sheet may be 8" wide and 12" long or very much larger and the casing may be omitted. The use of a sheet of paper in this fashion is useful for testing the various recording mechanisms for range of amplitude permissible, for the determination of the best polarizing current, and to form an estimation of fidelity. To gain more amplitude all the devices set out may be compounded and operate a connecting lever to add the effects; also they may be compounded laterally at an angle to gain lateral stiffness.

Referring now to all the devices, the subject matter of this invention, as regards the behavior of the magnetic material, some remarks may be made with regard to the expansionmagnetic field curves. Such curves, or graphs, may be seen in the Encyclopaedia Britannica, or in text books. It is possible that the change in length is more linear when referred to flux density or B rather than H. The constant potential system compels the flux density, over the working range, to follow the output voltage at the expense of complicated changes in the magnetizing current. The operation bears some resemblance to the use of valves in Class B amplification.

Although the wound cores have been treated as plain inductances, to fix ideas, it is of course realized that considerations of motional impedance may arise and this aspect has been ignored. The use of the invention is a matter of practice with theory as some guide.

The output valve system which has been used is one in which triodes working at 400 volts are in parallel and also in push-pull. The valves are operated in the Class A-B. I have also experimentally used pentodes in push-pull.

All the recording instruments herein can be altered, or used for lateral recording by well known adaptations. For instance bell-crank levers may besubstituted, or the axes and set of the stylus levers altered; moreover considerations of temperature changes have less weight. Thus the apparatus of Fig. 4 of the drawings which is a favored construction, is easily adapted for lateral operation. Here the floating weight I2 is swung out to the left and the sliding shoe modified for engagement with the disc blank.

What I claim is:

1. A magneto-strictive sound translator device comprising at least two elongated magneto-strictive members each composed throughout its length of a single predetermined magnetostrictive material whereby each of said members is adapted to expand and contract freely directly longitudinally under magneto-strictive action at acoustic frequencies, means anchoring said members and carrying the same each at one of its ends, a magnetic circuit including said members, a source of magneto-motive force included in said circuit comprising two acoustic energizing coils, one on each of said members, and providing therethrough a magnetic flux threading said members and exciting the same in phase opposition with respect to one another,

amines mechanical linking means between and connected at its ends to the unmountedunanchored ends of said members and combining the longitudinal movements thereof additively, andan acoustically vibratory member driven from said linking'means and responsive to said combined longitudinal movements through said linking means.

2. A. device according to claim 1' wherein the anchoring means ."carry the magnetostrictive members with 'theunanchored end of one adjacent that of the other and in which the magneticcircuit includes a divided polarizing magnetic circuit and 'i'sadapted to excite said magneto-strictive members simultaneously to expand the one and contract the other.

3. A device according to claim 1 wherein the anchoring means carry the ma-gneto-strictive members with the unanchored end of one adjacent that of the other and in which the magnetic circuit includes a divided polarizing magnetic circuit and is adapted to excite said magneto-'strictive members simultaneously to expand the one and contract theother, mechanical linking means connected between the adjacent ends of the magneto-strictive members and the acoustically vibratory member being driven from an intermediate connection on said linkin means.

4. A magneto-strictive sound translator device comprising at least two elongated magnetostrictive members each composed throughout its length of a single predetermined magnetostrictive material, whereby each of said members is adapted to expand and contract freely directly longitudinally under magneto-strictive action at acoustic frequencies, means anchoring said members and carrying the same each at one of its ends, a magnetic circuit includin said members, two acoustic energizing coils, oneon each of said members and providing therethrough a magnetic'fiux threading said members and exciting the same in phase opposition with respect to one another, mechanical linking means between and connected at its ends to the unmounted ends of said members and combining the longitudinal movements thereof additively, and an acoustically vibratory member driven from said linking means and responsive to said combined longitudinal movements through said linking means and a divided Polariz-ing circuit connected with said acoustic energizing coils.

5. A magneto-strictive sound translator device comprising at least two elongated magnetostrictive members "each composed throughout its length of a single predetermined magnetostrictive material w-h-ereby 'each of said members is adapted to expand and contract freely, directly longitudinally under jmagneto-strictive action at acoustic frequencies-mountin means of large mass relative to the mass of each of said elongated members carrying each" of ,said members at one of its ends with its other end adjacent "the unmounted end of the other of said members, spring means applying compression to one of said elongated members and tension to the other, a magnetic circuit including said members, a' -source of magneto-motive force included in said circuit and providing therein a magnetic flux threading said members and exciting :each of the same to expand and contract as .2, unit directly longitudinally *by magnetostrictive action, mechanical linking means mechanically linking the unmounted adjacent ends '16 movements thereof additively, and an acoustb cally vibratory member driven by the combined longitudinal movements through said mechanical linking means.

6. A magneto-strictive sound translator device comprising at least two elongated magneto-strictivememberseach composed throughout their lengths of a single predetermined magnetostrictive material whereby each of said-members is adapted to expand and contract freely, directly longitudinally under magneto-strictive action at acoustic frequencies, mounting means carrying each of said members at one of its ends "with its other end adacent the unmounted end of the other of said members, a magneticcircuit including said members, a source or" magnetomotive force included in said circuit and providing therein amag-netic flux threadingsaid members and exciting each of the same to. expand and contract as a unit directly longitudinally by magneto-strictive action, in phase opposition, said source including windings on said magnetic circuitgmechanical linking means mechanically linking the unmounted adjacent ends of said members and combining the longitudinal movements thereof additivel-y, and an acoustically vibratory member driven by the combinedlongitudina-l movements through. said "mechanical linking means.

'7. A magneto-stric-ti-ve sound translator device as set forth in claim 1 inv which said source of magneto-motive force is constituted by a'oonstant potential acoustic driving frequency.

8. A magneto-strictive sound translator de-' vice as set forth in claim 1 in which said source of magneto-motive force is constituted by a constant potential acoustic driving frequency and wherein said circuit includes anegative feed-back reaction coil.

9. A magneto-strictive :sound translator. device as set forth in claimzl in whichsaid source of-magneto-motive force is constituted by a constant potential acoustic driving frequem yand wherein said circuit includes a differentiating Gi-ICtllbffOl rendering the acoustic response of said devicesubstantially proportional to the input "1m pressed upon said circuit.

ADRIANERANCISSYKES.

' REFERENCES 'CITE'D The following references are of record in the file of thisepatentz UNITED STATES PATENTS Number "Name Date 436,514 Wiegand 'S ep't. 16,1890 1,821,836 Hull Sept. 1, 1.931 2,031,789 Pierce Feb; 25, 1936 2,113,907 Stykes i Apr. 12,1938 2,249,335 Lak-atos i July 22, 1941 12575028 Westerka-mr 'Sept.'2'3, 1941 2,418,132 Maxfield Apr'. 1, 1947 2,461,635 Feller Feb. '15, 1949 2,471,542 Rich i :31, 1,949 2,475,148 Massa .1Ju1y 5', 31,949 2,476,778 ,Smoluchowski 'Julyl'9, 1949 2,484,960 Rich Oct."1'8, 19119 23196384 Massa "Feb. 1'7, 1950 2,499,110 Rich Feb. 28, 195.0

FOREIGN PATENTS Number :Country Date 407,704 Great Britain .Mar. 21, 1934 490,826 GreatBritam Aug. 18,1938 5905733 Great Britain i-Dec. 21, 193;? 

